Wildfire propagation: a two-dimensional multiphase approach

This paper describes a multiphase approach for determining the rate of propagation of a line fire through a randomly-packed fuel bed of thermally-thin cellulosic particles and the induced hydrodynamics inside and above the litter. A set of time-dependent balance equations are solved for each phase (a gas phase and $N$ solid phases) and the coupling between the gas phase and the solid phases is rendered through exchange terms of mass due to the thermal degradation of the fuel material (heating, drying, pyrolysis, and char combustion), momentum, and energy. The radiative transfer equation in the fuel bed is deduced from the P1-approximation, and radiation from the flame to the fuel bed is accounted for with the help of the empirical model of Markstein. Kinetics is incorporated to describe pyrolysis and combustion processes. The solution is performed numerically by a finite-volume method. The development of a line fire from the moment of initiation to quasi-steady propagation is predicted and discussed. Results obtained by this multiphase model are compared to measurements made on laboratory fires using dead pine needles as fuel. The predicted rates of fire spread for some configurations including slope effects agree well with measured values.